Method for manufacturing arc tube body and core used in the method

ABSTRACT

To form an arc tube body including a main tube portion to be a discharge space and thin tube portions for accommodating electrodes, a core ( 6 ) is disposed in a hollow space formed by a pair of arc tube body formation molds ( 7 ) and ( 8 ) and thereafter, a slurry ( 12 ) is injected into a space between the molds ( 7 ), ( 8 ) and the core ( 6 ). In the core ( 6 ), portions for forming the internal shape of the thin tube portions of the arc tube body are provided with a shaft ( 3 ).

This application is a division of application Ser. No. 10/240,874, filedOct. 3, 2002, entitled METHOD FOR MANUFACTURING ARC TUBE BODY AND COREUSED IN THE METHOD.

TECHNICAL FIELD

The present invention relates to an arc tube body. In particular, thepresent invention relates to a method for manufacturing an arc tube bodyformed of a ceramic material and to a core used in the method.

BACKGROUND ART

Metal halide lamps have been known as metal vapor discharge lamps towhich reasonable mercury lamp ballasts are applicable. In general, aquartz arc tube body mainly is used in the metal vapor discharge lamps.However, in recent years, a ceramic arc tube body also is used toincrease the heat resistance of the metal vapor discharge lamps.

FIGS. 33A and 33B are cross-sectional views, each showing one example ofa conventional arc tube body formed of a ceramic material. FIG. 33Ashows a conventional arc tube body including a cylindrical main tubeportion 101, thin tube portions 102 a and 102 b for accommodating a pairof main electrodes, and ring-shaped members 103 for fixing the thin tubeportions 102 a and 102 b to the main tube portion 101 (see JP11(1999)-162416 A). On the other hand, FIG. 33B shows a conventional arctube body including a thin tube portion 102 c for accommodating anauxiliary electrode in addition to the same components as those in thearc tube body shown in FIG. 33A (see JP 10(1998)-106491 A).

In the arc tube body shown in FIG. 33A, the main tube portion 101 isformed by rubber pressing. On the other hand, in the arc tube body shownin FIG. 33B, the main tube portion 101 is formed by performing extrusionmolding and then blow molding. In the arc tube body shown in FIGS. 33Aand 33B, the thin tube portions 102 a, 102 b, and 102 c are formed byextrusion molding, and the ring-shaped members 103 are formed by diepressing. The components formed independently as described above areconnected with each other and then subjected to firing to complete anarc tube body.

However, the arc tube body shown in FIGS. 33A and 33B has the problemsas follows. In the arc tube body shown in FIGS. 33A and 33B, thecomponents are formed independently as described above. Therefore, whenthe arc tube body is used as an arc tube body of a metal vapor dischargetube, internal stress generated due to an increase in the internalpressure at the time of electric discharge is concentrated at theconnecting portions between the respective components. In particular,regions 104, which are within the connecting portions between the maintube portion 101 and the ring-shaped members 103 and in the vicinity ofthe inner walls of the main tube portion 101, have low mechanicalstrength. Thus, cracks may be generated in the reigns 104 due to theinternal stress.

In addition, in the case where components used for manufacturing an arctube body are formed independently as described above, the process forconnecting the components is required, which increases the cost formanufacturing the arc tube body.

As a solution to the above-mentioned problems, a slip casting method isproposed in which an arc tube body is formed integrally (see JP11(1999)-204086 A). FIG. 34 is a cross-sectional view of an arc tubebody formed by the conventional slip casting method. In FIG. 34,reference numeral 100 a denotes thin tube portions for accommodatingelectrodes, and reference numeral 100 b denotes a main tube portion toserve as a discharge space.

FIGS. 35 to 38 are cross-sectional views, each illustrating one processof the conventional slip casting method. It is to be noted that theprocesses illustrated from FIG. 35 through FIG. 38 are a series ofprocesses. Hereinafter, a method for manufacturing an arc tube bodyaccording to the conventional slip casting method will be described withreference to FIGS. 35 to 38.

First, as shown in FIG. 35, a slurry 111 containing ceramic powder, abinder, and water as main components is injected to fill a hollow spaceinside a plaster mold 110. The hollow space inside the plaster mold 110is formed so as to correspond to the external shape of an arc tube bodyto be manufactured.

Next, as shown in FIG. 36, only water from among the above-mentionedthree main components contained in the slurry 111 is absorbed in theplaster mold 110, and a mixture 112 of the ceramic powder and the binderare allowed to adhere to the inner surface of the plaster mold 110 untilit forms a sufficient thickness to provide a molded article with adesired thickness.

Subsequently, as shown in FIG. 37, excess slurry present in the hollowspace is drained and the mixture 112 adhered to the inner surface of theplaster mold 110 is dried. Thereafter, a molded article 113 is taken outof the plaster mold 110. The molded article 113 is then subjected to anafter processing such as firing. Thus, an arc tube body as shown in FIG.34 can be obtained.

However, the slip casting method illustrated by FIGS. 35 to 38 has thefollowing problem. When forming a small arc tube body of a low wattage,e.g., 70 W or less, thin tube portions 100 a (see FIG. 34) are formed tobe very thin. Thus, the thin tube portions 100 a may be broken whenbeing taken out from the plaster mold 110 or during transport.

Further, in the slip casting method illustrated by FIGS. 35 to 38, thearc tube body is formed by having water absorbed in the plaster mold110, thereby adhering the mixture of the ceramic powder and the binderto the surface of the plaster mold 110. Therefore, from a macroscopicviewpoint, it can be said that this method can produce an arc tube bodywith a uniform thickness only. On this account, it is difficult to makeonly the thickness of tapered portions at the boundaries between therespective thin tube portions 100 and the main tube portion 100 bgreater than the thickness of other portions, for example.

Even in the case where an arc tube body is formed by the above-mentionedslip casting method, the thickness of the arc tube body can be changedpartially by mechanically processing the molded article, for example.However, such mechanical processing increases the cost for manufacturingthe arc tube body.

Further, a luminescent lamp provided with an arc tube body manufacturedaccording to the slip casting method illustrated by FIGS. 35 to 38 mayfail to light up. The reason for this is considered that calciumcontained in the plaster mold 110 as a main component may adhere to thesurface of the hollow molded article 113, which is to be processed intoan arc tube body.

Therefore, it is an object of the present invention to solve theabove-mentioned problems and to provide a method for manufacturing anarc tube body, capable of forming an arc tube body integrally and ofreducing the chances that thin tube portions of the arc tube body mightbe broken, and a core used in the method.

DISCLOSURE OF INVENTION

In order to achieve the above object, a method for manufacturing an arctube body according to the present invention is a method formanufacturing an arc tube body, which includes a main tube portion to bea discharge space and thin tube portions for accommodating electrodes,using a pair of molds and a material to be injected thereinto. Themethod includes at least disposing a core in a hollow space formed bythe molds before injecting the material, and the core includes portionsfor forming an internal shape of the thin tube portions, a portion forforming an internal shape of the main tube portion, and a shaft disposedin the portions for forming an internal shape of the thin tube portions.

In the above-mentioned method for manufacturing an arc tube bodyaccording to the present invention, it is preferable that the molds areformed of a metallic material, a resin material, or a ceramic materialand that the material to be injected into a space between the molds andthe core is a slurry containing ceramic powder, a solvent, and ahardening agent as main components. Preferably, the above-mentionedmethod further includes: forming a hardened slurry by solidifying theslurry injected into the hollow space where the core is disposed; takingout the hardened slurry integrated with the core from the molds andseparating the hardened slurry and the core; and firing the hardenedslurry from which the core has been separated.

Further, the above-mentioned method for manufacturing an arc tube bodyaccording to the present invention preferably includes disposing theshaft in a hollow space formed by a pair of core formation molds andfilling the hollow space with a fusible material or a combustiblematerial so that at least a portion of the core for forming an internalshape of the main tube portion of the arc tube body is formed of thefusible material or the combustible material.

Furthermore, in the above-mentioned method for manufacturing an arc tubebody according to the present invention, it is preferable that the corecomprises two portions for forming an internal shape of the thin tubeportions, one of the two portions facing the other portion with theportion for forming the main tube portion intervening therebetween, anda shaft present at one of the two portions and a shaft present at theother portion are defined by one common shaft. The core may comprise atleast two shafts.

In the above-mentioned method for manufacturing an arc tube bodyaccording to the present invention, a layer of a fusible material or acombustible material may be formed around the shaft. The shaft may beformed of a metallic material, a resin material, or a ceramic material.Further, in the case where the shaft is formed of a material thatgenerates heat when an electric current is applied thereto, heatgenerated from the shaft melts a portion formed of the fusible materialof the core, thereby allowing the hardened slurry and the core to beseparated from each other.

Next, in order to achieve the above object, a core used formanufacturing an arc tube body according to the present invention is acore used for manufacturing an arc tube body, which comprises a maintube portion to be a discharge space and thin tube portions foraccommodating electrodes, using a pair of molds and a material to beinjected thereinto, and the core is disposed in a hollow space formed bythe pair of molds before injecting the material. The core according tothe present invention includes portions for forming an internal shape ofthe thin tube portions, a portion for forming an internal shape of themain tube portion, and a shaft disposed in the portions for forming aninternal shape of the thin tube portion.

In the above-mentioned core according to the present invention, it ispreferable that the portion for forming an internal shape of the maintube portion is formed of a fusible material or a combustible material.It is also preferable that the core comprises two portions for formingan internal shape of the thin tube portions, one of the two portionsfacing the other portion with the portion for forming the main tubeportion intervening therebetween, and a shaft present at one of the twoportions and a shaft present at the other portion are defined by onecommon shaft.

Further, in the above-mentioned core according to the present invention,the core may include at least two shafts. Further, the portions forforming an internal shape of the thin tube portions may be formed byforming a layer of a fusible material or a combustible material aroundthe shaft. Furthermore, the shaft may be formed of a metallic material,a resin material, or a ceramic material. Alternatively, the shaft may beformed of a material that generates heat when an electric current isapplied thereto.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view illustrating one process of a methodfor manufacturing an arc tube body according to Embodiment 1.

FIG. 2 is a cross-sectional view illustrating another process of themethod for manufacturing an arc tube body according to Embodiment 1.

FIG. 3 is a cross-sectional view illustrating another process of themethod for manufacturing an arc tube body according to Embodiment 1.

FIG. 4 is a cross-sectional view illustrating another process of themethod for manufacturing an arc tube body according to Embodiment 1.

FIG. 5 is a cross-sectional view illustrating another process of themethod for manufacturing an arc tube body according to Embodiment 1.

FIG. 6 is a cross-sectional view illustrating another process of themethod for manufacturing an arc tube body according to Embodiment 1.

FIG. 7 is a cross-sectional view illustrating another process of themethod for manufacturing an arc tube body according to Embodiment 1.

FIG. 8 is a cross-sectional view illustrating another process of themethod for manufacturing an arc tube body according to Embodiment 1.

FIG. 9 is a cross-sectional view illustrating another process of themethod for manufacturing an arc tube body according to Embodiment 1.

FIG. 10 is a cross-sectional view illustrating another process of themethod for manufacturing an arc tube body according to Embodiment 1.

FIG. 11 is a cross-sectional view illustrating one process of a methodfor manufacturing an arc tube body according to Embodiment 2.

FIG. 12 is a cross-sectional view illustrating another process of themethod for manufacturing an arc tube body according to Embodiment 2.

FIG. 13 is a cross-sectional view illustrating another process of themethod for manufacturing an arc tube body according to Embodiment 2.

FIG. 14A is a cross-sectional view illustrating another process of themethod for manufacturing an arc tube body according to Embodiment 2, and

FIG. 14B is a cross-sectional view of the same in which projections areformed on thin tube formation portions of a core.

FIG. 15 is a cross-sectional view illustrating one process of a methodfor manufacturing an arc tube body according to Embodiment 3.

FIG. 16 is a cross-sectional view illustrating another process of themethod for manufacturing an arc tube body according to Embodiment 3.

FIG. 17 is a cross-sectional view of a core used in the method formanufacturing an arc tube body according to Embodiment 3.

FIG. 18A is a cross-sectional view illustrating one process of a methodfor manufacturing an arc tube body according to Embodiment 4, and FIG.18B is a cross-sectional view taken along the cutting plane line A-A′ ofFIG. 18A.

FIG. 19A is a cross-sectional view illustrating another process of themethod for manufacturing an arc tube body according to Embodiment 4, andFIG. 19B is a cross-sectional view taken along the cutting plane lineB-B′ of FIG. 19A.

FIG. 20A is a cross-sectional view illustrating another process of themethod for manufacturing an arc tube body according to Embodiment 4, andFIG. 20B is a cross-sectional view taken along the cutting plane lineC-C′ of FIG. 20A.

FIG. 21A is a cross-sectional view illustrating another process of themethod for manufacturing an arc tube body according to Embodiment 4, andFIG. 21B is a cross-sectional view taken along the cutting plane lineD-D′ of FIG. 21A.

FIG. 22A is a cross-sectional view illustrating another process of themethod for manufacturing an arc tube body according to Embodiment 4, andFIG. 22B is a cross-sectional view taken along the cutting plane lineE-E′ of FIG. 22A.

FIG. 23A is a cross-sectional view illustrating another process of themethod for manufacturing an arc tube body according to Embodiment 4, andFIG. 23B is a cross-sectional view taken along the cutting plane lineF-F′ of FIG. 23A.

FIG. 24 is a cross-sectional view illustrating another process of themethod for manufacturing an arc tube body according to Embodiment 4.

FIG. 25 is a cross-sectional view illustrating another process of themethod for manufacturing an arc tube body according to Embodiment 4.

FIG. 26 is a cross-sectional view illustrating another process of themethod for manufacturing an arc tube body according to Embodiment 4.

FIG. 27A is a cross-sectional view illustrating one process of a methodfor manufacturing an arc tube body according to Embodiment 5, and FIG.27B is a cross-sectional view taken along the cutting plane line G-G′ ofFIG. 27A.

FIG. 28A is a cross-sectional view illustrating another process of themethod for manufacturing an arc tube body according to Embodiment 5, andFIG. 28B is a cross-sectional view taken along the cutting plane lineH-H′ of FIG. 28A.

FIG. 29A is a cross-sectional view illustrating another process of themethod for manufacturing an arc tube body according to Embodiment 5, andFIG. 29B is a cross-sectional view taken along the cutting plane lineI-I′ of FIG. 29A.

FIG. 30 is a cross-sectional view illustrating one process of a methodfor manufacturing an arc tube body according to Embodiment 6.

FIG. 31A is a view of a core used in the method for manufacturing an arctube body according to Embodiment 7; FIG. 31B is a view of an arc tubebody manufactured by the method for manufacturing an arc tube bodyaccording to Embodiment 7.

FIG. 32A is a view of a core used in a method for manufacturing an arctube body according to Embodiment 8; FIG. 32B is a view of an arc tubebody manufactured by the method for manufacturing an arc tube bodyaccording to Embodiment 8.

FIGS. 33A and 33B are cross-sectional views, each showing one example ofa conventional arc tube body formed of a ceramic material.

FIG. 34 is a cross-sectional view of an arc tube body formed byconventional slip casting method.

FIG. 35 is a cross-sectional view illustrating one process ofconventional slip casting method.

FIG. 36 is a cross-sectional view illustrating another process ofconventional slip casting method.

FIG. 37 is a cross-sectional view illustrating another process of theconventional slip casting method.

FIG. 38 is a cross-sectional view illustrating another process of theconventional slip casting method.

FIG. 39 is a schematic view showing a configuration of a metal vapordischarge lamp provided with an arc tube body according to Embodiment 1.

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1

Hereinafter, a method for manufacturing an arc tube body and a core usedin the method according to Embodiment 1 will be described with referenceto FIGS. 1 to 10. FIGS. 1 to 10 are cross-sectional views, eachillustrating one process of the method for manufacturing an arc tubebody according to Embodiment 1. It is to be noted that the processesillustrated from FIG. 1 through FIG. 10 are a series of processes. Themanufacturing method according to Embodiment 1 includes processes formanufacturing a core according to Embodiment 1. Among FIGS. 1 to 10,FIGS. 1 to 4 illustrate a series of processes for manufacturing a coreaccording to Embodiment 1.

The method for manufacturing an arc tube body according to Embodiment 1includes placing a core according to Embodiment 1 in a hollow spaceformed by a pair of molds for forming an arc tube body (hereinafter,referred to as “arc tube body formation molds”) and then injecting amaterial into a space between the arc tube body formation molds and thecore. An arc tube body obtained by this method includes a main tubeportion to serve as a discharge space and a pair of (i.e., two) thintube portions for accommodating electrodes (see FIG. 10, which will bedescribed later).

First, as shown in FIG. 1, molds 1 and 2 for forming a core(hereinafter, referred to as “core formation molds”) are provided. Thecore formation mold 1 has a recess 1 a and the core formation mold 2 hasa recess 2 a. Accordingly, when the core formation molds 1 and 2 arebonded to each other, a hollow space is formed by the recesses 1 a and 2a. The recesses 1 a and 2 a are formed so that they can form a hollowspace corresponding to the shape of a core to be formed.

As described later, a firing process and the like are performed tocomplete an arc tube body. Further, the internal shape of the arc tubebody is formed by the core. Therefore, the recesses 1 a and 2 a areformed considering the shrinkage of the arc tube body after firing sothat the arc tube body will have a predetermined internal shape afterfiring.

Reference numeral 5 is an inlet through which a material is injected.The inlet 5 is provided so that the material flows into the hollow spacefrom the central portion of the recess 2 a. In Embodiment 1, the coreformation molds 1 and 2 are formed of stainless steel. However, thematerial of the core formation molds 1 and 2 is not limited to stainlesssteel, and can be other metallic materials such as aluminum and thelike; resin materials such as acrylate, nylon, and the like; or ceramicmaterials containing no calcium, such as alumina and the like.

Next, as shown in FIG. 2, the core formation molds 1 and 2 are bonded toeach other, and a shaft 3 is disposed in the hollow space formed by therecesses 1 a and 2 a. The shaft 3 is disposed in such a manner that thecentral axis thereof coincides with the central axis of a core to beformed. Every portion of the shaft 3 except for the central portion isin close contact with the core formation molds 1 and 2. In Embodiment 1,one core wire formed of a resin material is used as the shaft 3. Thisshaft 3 will be the central axis of a core to be obtained. The shaft 3may be formed of a material other than the resin material, such as ametallic material, a ceramic material, etc. The diameter of the shaft 3has an effect on the inner diameter of an arc tube body to be obtained,and thus is determined considering the shrinkage after firing.

Then, as shown in FIG. 3, the hollow space where the shaft 3 is disposedis filled with a fusible material 4. In Embodiment 1, paraffin wax(melting point: 70° C.) is used as the fusible material 4. The paraffinwax that has been heated and melted at 90° C. is injected into thehollow space through the inlet 5. After the injection, the coreformation molds 1 and 2 holding the fusible material 4 are left untilthey cool down to room temperature so that the fusible material 4 issolidified.

After that, as shown in FIG. 4, the bonded core formation molds 1 and 2are separated from each other to obtain a core 6. The core 6 includes aportion 6 b for forming an internal shape of a main tube portion of anarc tube body (hereinafter, referred to as a “main tube formationportion”) and portions 6 a for forming an internal shape of thin tubeportions of an arc tube body (hereinafter, referred to as “thin tubeformation portions”). In Embodiment 1, the core 6 includes two thin tubeformation portions 6 a, one of the thin tube formation portions 6 afacing the other thin tube formation portion 6 a with the main tubeformation portion 6 b intervening therebetween.

In the core 6 according to Embodiment 1, only the main tube formationportion 6 b is formed of the fusible material 4. The thin tube formationportions 6 a are formed of the shaft 3 only, and include no fusiblematerial 4. The shaft present at one thin tube formation portion 6 a andthe shaft present at the other thin tube formation portion 6 a aredefined by one common shaft 3.

A solidified fusible material 4 a present at a portion from which thefusible material 4 is injected (i.e., inside the inlet 5) is cut fromthe core 6 when separating the core formation molds 1 and 2. However,since the portion of the core 6 from which the fusible material 4 a hasbeen cut has a great surface roughness, it is necessary to polish thecore 6 to the required extent.

Subsequently, as shown in FIG. 5, an arc tube body formation mold 7having a recess 7 a and an arc tube body formation mold 8 having arecess 8 a are provided, and the core 6 obtained in the above-mentionedmanner is disposed in a hollow space formed by the recesses 7 a and 8 a.The recesses 7 a and 8 a are formed so that they can form a hollow spacecorresponding to the shape of an arc tube body to be formed. Thus, aspace 13 for forming an arc tube body is formed between the respectiverecesses 7 a, 8 a and the core 6.

A molded article formed using the arc tube body formation molds 7, 8 andthe core 6 turns into an arc tube body after being subjected to firing.Therefore, the recesses 7 a and 8 a are formed considering the shrinkageof the molded article after firing so that an arc tube body having apredetermined external shape is obtained after firing. In Embodiment 1,the arc tube body formation molds 7 and 8 are formed of stainless steel.However, the material of the arc tube body formation molds 7 and 8 isnot limited to stainless steel, and can be other metallic materials;resin materials; and ceramic materials.

When disposing the core 6 in the hollow space, if the positionadjustment of the core 6 with respect to the arc tube body formationmolds 7 and 8 is insufficient, an arc tube body to be obtained will havea nonuniform thickness. On this account, in the present embodiment, oneend of the shaft 3 is inserted into and fixed to a hole formed byrecesses 7 b and 8 b formed in the arc tube body formation molds 7 and8, respectively. Further, a plate member 9 for positioning, which isprovided with a hole 10 having the same diameter as the shaft 3, isattached to the bonded outer surfaces of the arc tube body formationmolds 7 and 8 on the side of the other end of the shaft 3, and the otherend of the shaft 3 is inserted into and fixed to the hole 10. Accordingto this configuration, the position adjustment of the core 6 withrespect to the arc tube body formation molds 7 and 8 can be carried outwith high precision. Reference numeral 11 denotes positioning pins forfixing the plate member 9 to the arc tube body formation molds 7 and 8.

Next, as shown in FIG. 6, a slurry 12 containing ceramic powder, asolvent, and a hardening agent as main components is injected into thespace 13. The slurry 12 will be a main component of an arc tube body tobe obtained. In Embodiment 1, the slurry 12 is prepared in the followingmanner. First, 100 parts by weight of alumina powder is mixed with 0.05part by weight of magnesium oxide as an additive, 1.0 part by weight ofpolycarboxylate as a dispersing agent, 10 parts by weight of awater-soluble epoxy resin as a hardening agent, and 25 parts by weightof water as a solvent in a vessel. Then, 2 parts by weight of anamine-based hardening agent that reacts with the water-soluble epoxyresin to cause hardening is added to and mixed with the resultantmixture in the vessel. Thus, the slurry 12 is prepared.

After the slurry 12 is injected into the space 13, the arc tube bodyformation molds 7 and 8 are left for 2 days at room temperature. Theslurry 12 is solidified by the action of the hardening agent, thusgiving a hardened slurry 14. In Embodiment 1, the epoxy resin is used asa hardening agent. However, the hardening resin is not limited thereto,and can be, for example, phenol resins, urea resins, urethane resins,and the like that can be hardened at room temperature or by heating. Thesame effect can be obtained when these resins are used as a hardeningagent.

Further, in Embodiment 1, the slurry is hardened by the action of thehardening agent. However, the slurry may be hardened by other actions,such as a sol-gel transition, for example. It is also possible to hardenthe slurry by forming cross-linked polymers. This can be achieved byadding monomers to the slurry and then causing the radicalpolymerization of the monomers.

Then, as shown in FIG. 7, the arc tube body formation molds 7 and 8 areseparated from each other to take out the hardened slurry 14 integratedwith the core 6. Further, as shown in FIG. 8, the shaft 3 is pulled outfrom the hardened slurry 14 integrated with the core 6. In this manner,the hardened slurry 14 with the solidified fusible material 4 remaininginside can be obtained.

In Embodiment 1, the shaft 3 forming the core 6 may be formed of amaterial that generates heat when a current is applied thereto, e.g., anichrome wire and the like. When the shaft 3 is formed of such amaterial, it is possible to melt the fusible material 4 around the shaft3 by applying a current from both ends of the shaft 3 to cause the shaft3 to generate heat. The adhesion between the shaft 3 and the fusiblematerial 4 thus becomes weaker, which allows the shaft 3 to be removedeasily.

The shaft 3 also may be formed of a material having high thermalconductivity. When the shaft 3 is formed of such a material, it ispossible to melt the fusible material 4 around the shaft 3 by conductingheat from both ends of the shaft 3. Thus, similarly to the case of thenichrome wire as described above, the adhesion between the shaft 3 andthe fusible material 4 becomes weaker, which allows the shaft 3 to beremoved easily.

Subsequently, the hardened slurry 14 with the fusible material 4remaining inside is placed in a constant temperature bath set at 90° C.so that the solidified fusible material 4 is melted and drained from thehardened slurry 14, as shown in FIG. 9. Then, the hardened slurry 14,which is hollow after the fusible material 4 has been drained, is keptat 400° C. for 5 hours in the air so that an organic constituentcontained therein is decomposed and evaporated off. After that, thehardened slurry 14 is subjected to pre-firing at 1300° C. for 2 hours.The hardened slurry 14 thus pre-fired is then fired at 1900° C. for 2hours in a hydrogen atmosphere so that the hardened slurry 14 issintered.

Through the above-mentioned processes, eventually, a translucent arctube body 16 for a metal vapor discharge lamp as shown in FIG. 10 can beobtained. In FIG. 10, reference numeral 16 a denotes thin tube portionsfor accommodating electrodes, and reference numeral 16 b denotes a maintube portion to serve as a discharge space.

As described above, a method for manufacturing an arc tube bodyaccording to Embodiment 1 is characterized in that the core 6 includingthe thin tube formation portions 6 a defined by the shaft 3 is used (seeFIGS. 5 to 7). Accordingly, the inner diameter of the thin tube portions16 a of the arc tube body 16 can be controlled by selecting the outerdiameter of the shaft 3. As a result, an arc tube body including thintube portions that are thinner than those in conventional arc tubebodies can be obtained. In addition, since the core is provided with theshaft 3, the chances that the portions to be the thin tube portions 16 ain the molded article might be broken due to the force applied whenseparating the arc tube body formation molds 7 and 8, vibrations duringthe transportation, etc., can be reduced.

Further, in an arc tube body for a metal vapor discharge lamp of arelatively low wattage, e.g., 70 W, the thin tube portions 16 a are verylong and narrow. For example, they are about 0.8 mm in inner diameterand about 25 mm in length. In this case, the diameter of the thin tubeformation portions 6 a of the core 6 is required to be about 1 mm.Therefore, in the case where a core formed of a soft material is used,long and narrow portions, i.e., the thin tube formation portions, areliable to be broken, resulting in a considerably reduced manufacturingyield. However, in Embodiment 1, since the thin tube formation portionsinclude the shaft 3 as described above, the chances that the thin tubeformation portions might be broken can be reduced, which causes theproductivity to be improved remarkably.

As described above, the conventional slip casting method has the problemthat it can produce an arc tube body with a uniform thickness only andrequires a mechanical processing after the formation or the firing ofthe arc tube body in order to change the thickness of the arc tube bodyas desired. In contrast, in Embodiment 1, it is possible to design thethickness of an arc tube body as desired by changing the shape of thecore 6.

This will be described by taking the following case as an example. InFIG. 10, the thickness “tp” of the tapered portion of the main tubeportion 16 b at the boundaries between the respective thin tube portions16 a and the main tube portion 16 b is desired to be greater than thethickness “ts” of the straight central portion of the main tube portion16 b. This can be achieved by designing the shape of the core 6 so that,in FIG. 5, the distance “lp” between a tapered portion 17 of the core 6and the arc tube body formation mold 7 or 8 is greater than the distance“ls” between a straight portion 18 of the core 6 and the arc tube bodyformation mold 7 or 8.

The transmittance and the mechanical strength of the arc tube body 16obtained in the above-mentioned manner were measured. As a result, itwas found that the thus-obtained arc tube body 16 had the transmittanceand the mechanical strength equivalent to those of the conventional arctube body manufactured by the above-mentioned slip casting method. Also,the composition of the arc tube body 16 was analyzed. As a result, itwas confirmed that the arc tube body 16 contained no calcium. This isbecause the arc tube body 16 was formed using the metal molds made ofstainless steel as the core formation molds 1 and 2 and as the arc tubebody formation molds 7 and 8.

Further, 100 samples of the arc tube body 16 shown in FIG. 10 weremanufactured, and then, 100 samples of the metal vapor discharge lampshown in FIG. 39 were manufactured using the samples of the arc tubebody 16 to conduct a lighting test. FIG. 39 is a schematic view showinga configuration of the metal vapor discharge lamp provided with the arctube body according to Embodiment 1.

As shown in FIG. 39, the arc tube body 16 is contained in an outer tube120, which is closed on one end and open on the other end. Lead wires124 a and 124 b are provided in the two thin tube portions of the arctube body 16 so as to be connected to electrodes (not shown) placedinside the arc tube body 16. A lamp base 121 is attached to the open endof the outer tube 120. Reference numerals 122 a and 122 b are stem leadsextending from a stem 122. The stem lead 122 a is connected to the leadwire 124 a, and the stem lead 122 b is connected to the lead wire 124 bvia a power supply wire 123.

The lighting test showed that none of the sample lamps failed to lightup. Thus, it is understood that an arc tube body manufactured by themethod according to Embodiment 1 has good quality. In contrast, in thecase of the metal vapor discharge lamp provided with an arc tube bodymanufactured by the conventional method, 5 out of 100 samples failed tolight up.

FIGS. 1 to 10 shows an example in which paraffin wax is used as thefusible material 4 for forming the core 6. Here, an arc tube body wasmanufactured in the same manner as that shown in FIGS. 1 to 10 exceptthat a core was formed using an ethylene-vinyl acetate resin, which canbe heated and melted around 100° C., in place of paraffin wax.

In this case, an arc tube body having the same size, the same shape, andthe same ceramic characteristics as those of the arc tube body 6 shownin FIG. 10 could be obtained. Needless to say, in Embodiment 1, anyresin that can be heated and melted at a low temperature, e.g.,polyethylene resins, can be used as a material for forming a core, andthe same effect can be obtained even in the case where materials otherthan the wax and the ethylene-vinyl acetate resin are used.

Embodiment 2

Hereinafter, a method for manufacturing an arc tube body and a core usedin the method according to Embodiment 2 will be described with referenceto FIGS. 11 to 14. FIGS. 11 to 14 are cross-sectional views, eachillustrating one process of the method for manufacturing an arc tubebody according to Embodiment 2. It is to be noted that the processesillustrated from FIG. 11 through FIG. 14 are a series of processes.

In the method for manufacturing an arc tube body according to Embodiment2, an arc tube body is manufactured by injecting a material into arctube body formation molds, similarly to the method according toEmbodiment 1. An arc tube body manufactured by the method according toEmbodiment 2 has the same configuration as that of the arc tube bodyshown in FIG. 10. Embodiment 2 differs from Embodiment 1 in that a layerof a fusible material covers a shaft also at thin tube formationportions of a core. In other words, in Embodiment 2, the thin tubeformation portions of the core include a shaft and a fusible material.

First, a core formation mold 21 having a recess 21 a and a coreformation mold 22 having a recess 22 a are provided. The core formationmolds 21 and 22 are bonded to each other, and a shaft 23 is disposed inthe hollow space formed by the recesses 21 a and 22 a, as shown in FIG.11.

Similarly to the core formation molds used in Embodiment 1, the recesses21 a and 22 a are formed considering the shrinkage of an arc tube bodyafter firing. In Embodiment 2, the core formation molds 21 and 22 alsoare formed of stainless steel. However, as in Embodiment 1, the materialof the core formation molds 21 and 22 is not limited to stainless steel.Unlike Embodiment 1, a core wire formed of stainless steel is used asthe shaft 23. Further, unlike Embodiment 1, the shaft 23 is not incontact with the recesses 21 a and 22 a.

Next, as shown in FIG. 12, the hollow space where the shaft 23 isdisposed is filled with a fusible material 24. Also in Embodiment 2,paraffin wax is used as the fusible material 24 as in Embodiment 1. Thefusible material 24 is injected into the hollow space through an inlet25. After the injection, the core formation molds 21 and 22 holding thefusible material 24 are left until they cool down to room temperature sothat the fusible material 24 is solidified.

After that, as shown in FIG. 13, the bonded core formation molds 21 and22 are separated from each other to obtain a core 26. The core 26 thusobtained includes two thin tube formation portions 26 a and one maintube formation portion 26 b intervening therebetween, similarly to thecore 6 used in Embodiment 1. However, Embodiment 2 differs fromEmbodiment 1 in that not only the main tube formation portion 26 b butalso the thin tube formation portions 26 a are formed using the fusiblematerial 24.

In Embodiment 2, the inlet 25 is not provided so that the material flowsinto the main tube formation portion 26 b as in Embodiment 1, but isprovided so that the material flows into the hollow space from an end ofone of the thin tube formation portions 26 a. Therefore, a portion forforming a main tube portion of an arc tube body (the main portion has agreat effect on the lamp characteristics), i.e., the tube formationportion 26 b, does not have a rough surface as in Embodiment 1, whicheliminates the necessity of polishing the core as required in Embodiment1.

It is to be noted that, in Embodiment 2, the inlet 25 may be provided sothat the material flows into the main tube formation portion 26 b as inEmbodiment 1. In this case, it is still possible to obtain the core 26in which not only the main tube formation portion 26 b but also the thintube formation portions 26 a are formed using the fusible material 24 asshown in FIG. 13.

Subsequently, as shown in FIG. 14A, an arc tube body formation mold 27having a recess 27 a and an arc tube body formation mold 28 having arecess 28 a are provided, and the core 26 obtained in theabove-mentioned manner is disposed in a hollow space formed by therecesses 27 a and 28 a. The core 26 is disposed in the same manner asshown in FIG. 5 of Embodiment 1, and the arc tube body formation molds27 and 28 also have recesses 27 b and 28 b for positioning,respectively.

Thereafter, a slurry is injected into a space 30 for forming an arc tubebody and is solidified; a hardened slurry integrated with the core 26 istaken out from the arc tube body formation molds 27 and 28; and thehardened slurry integrated with the core 26 is fired after the shaft 23and the fusible material 24 forming the core 26 have been removed, inthe same manner as that in Embodiment 1 (see FIGS. 6 to 9). Thus, an arctube body similar to that of Embodiment 1 can be obtained (see FIG. 10).The slurry used in Embodiment 2 is the same as that used in Embodiment1.

As described above, the method for manufacturing an arc tube bodyaccording to Embodiment 2 also is characterized in that a core includinga shaft at thin tube formation portions is used, similarly to the methodaccording to Embodiment 1. Therefore, Embodiment 2 can produce the sameeffects as those described in Embodiment 1.

However, Embodiment 2 can produce another effect in addition to theeffects as described in Embodiment 1. Specifically, Embodiment 2 canprovide a high degree of freedom in the design of the internal shape ofthin tube portions of an arc tube body, i.e., in the design of theexternal shape of the core 26. For example, by providing recesses in aportion for forming the thin tube formation portions 26 a of the coreformation molds 21 and 22 shown in FIGS. 11 to 13, projections 29 asshown in FIG. 14B easily can be provided in the thin tube formationportions of the core. Accordingly, the internal shape of thin tubeportions of an arc tube body easily can be designed so as to have arecess and a projection in the middle portions thereof.

Further, in Embodiment 1, the shaft of the core needs to be removed fromthe hardened slurry before removing the fusible material. In contrast,in Embodiment 2, the hardened slurry may be heated without removing theshaft 23, and the shaft 23 can be removed together with the fusiblematerial 24.

Embodiment 3

Hereinafter, a method for manufacturing an arc tube body and a core usedin the method according to Embodiment 3 will be described with referenceto FIGS. 15 to 17. FIGS. 15 and 16 are cross-sectional views, eachillustrating one process of the method for manufacturing an arc tubebody according to Embodiment 3. It is to be noted that the processesillustrated from FIG. 15 through FIG. 16 are a series of processes. FIG.17 is a cross-sectional view of a core used in a method formanufacturing an arc tube body according to Embodiment 3.

First, a core formation mold 31 having a recess 31 a and a coreformation mold 32 having a recess 32 a are provided. The core formationmolds 31 and 32 are bonded to each other, and a shaft 33 is disposed inthe hollow space formed by the recesses 31 a and 32 a, as shown in FIG.15. Reference numeral 35 is an inlet through which a material isinjected.

In Embodiment 3, the core formation molds 31 and 32 have the same shapeas the core formation molds used in the Embodiment 2. However,Embodiment 3 differs from Embodiment 2 in that the core formation molds31 and 32 are formed of silicone rubber. Embodiment 3 also differs fromEmbodiment 2 in that a ceramic core wire formed of alumina is used asthe shaft 33.

Next, as shown in FIG. 16, the hollow space where the shaft 33 isdisposed is filled with a fusible material 34. In Embodiment 3, thefusible material 34 is spray-dry granule powder prepared by mixingcarbon power with a butyral resin as a binder. The fusible material 34is introduced into the hollow space through the inlet 35.

Subsequently, so-called rubber pressing is performed by applying apressure of 1800 kg/cm² to the side face 31 b of the core formation mold31 and the side face 32 b of the core formation mold 32 isostaticallyand hydrostatically. After that, the bonded core formation molds 31 and32 are separated from each other to obtain a core 36 as shown in FIG.17. Similarly to the core used in Embodiment 2, the core 36 includes ashaft 33 along its central axis, and not only the main tube formationportion 36 b but also the thin tube formation portions 36 a are formedusing the fusible material 34.

Thereafter, the thus-obtained core 36 is disposed in arc tube bodyformation molds; a slurry is injected into the arc tube body formationmolds and solidified; the hardened slurry integrated with the core istaken out from the arc tube body formation molds; and the shaft 33forming the core 36 is removed, in the same manner as that in Embodiment1 (FIGS. 6 to 8). Then, the hardened slurry is kept at 400° C. for 5hours in the air so that an organic constituent contained therein isdecomposed and evaporated off, after which the hardened slurry furtheris kept at 600° C. for 10 hours in the air so that carbon is decomposedby heat. Thus, the core 36 completely is removed from the hardenedslurry integrated with the core 36 (see FIG. 9).

After that, the hardened slurry from which the core has been removedcompletely is subjected to pre-firing at 1300° C. for 2 hours in theair, and further to firing at 1900° C. for 2 hours in a hydrogenatmosphere so that the hardened slurry is sintered. Thus, an arc tubebody similar to that of Embodiment 1 can be obtained (see FIG. 10). Theslurry used in Embodiment 3 is the same as that used in Embodiment 1.

As described above, the method for manufacturing an arc tube bodyaccording to Embodiment 3 also is characterized in that a core includinga shaft at thin tube formation portions is used, similarly to the methodaccording to Embodiment 1. Therefore, Embodiment 3 can produce the sameeffects as those described in Embodiment 1. In addition, Embodiment 3also can produce the same effects as those described in Embodiment 2.

Embodiment 4

Hereinafter, a method for manufacturing an arc tube body and a core usedin the method according to Embodiment 4 will be described with referenceto FIGS. 18A and 18B to 26A and 26B. FIGS. 18A and 18B to 26A and 26Bare cross-sectional views, each illustrating one process of the methodfor manufacturing an arc tube body according to Embodiment 4. It is tobe noted that the processes illustrated from FIGS. 18A and 18B throughFIGS. 26A and 26B are a series of processes.

The manufacturing method according to Embodiment 4 includes processesfor manufacturing a core according to Embodiment 4. Among FIGS. 18A and18B to 26A and 26B, FIGS. 18A and 18B to 20A and 20B illustrate a seriesof processes for manufacturing a core according to Embodiment 4.Further, in FIGS. 18A and 18B to 23A and 23B, FIGS. 18B to 23B arecross-sectional views taken along the cutting plane line (line A-A′ toline F-F′) of FIGS. 18A to 23B.

In the method for manufacturing an arc tube body according to Embodiment4, an arc tube body is manufactured by injecting a material into arctube body formation molds, similarly to the method according toEmbodiment 1. However, Embodiment 4 differs from Embodiment 1 in thatone of the thin tube portions is designed so as to accommodate twoelectrodes.

First, a core formation mold 41 having a recess 41 a and a coreformation mold 42 having a recess 42 a are provided. The core formationmolds 41 and 42 are bonded to each other, and a shaft 43 is disposed inthe hollow space formed by the recesses 41 a and 42 a, as shown in FIGS.18A and 18B. Also in Embodiment 4, the recesses 41 a and 42 a are formedconsidering the shrinkage of an arc tube body after firing. Referencenumeral 45 is an inlet. In Embodiment 4, the core formation molds 41 and42 also are formed of stainless steel. However, similarly to Embodiment1, the material of the core formation molds 41 and 42 is not limited tostainless steel.

In Embodiment 4, thin tube portions of an arc tube body are designed soas to accommodate three electrodes as shown in FIG. 26, which will bedescribed later. Accordingly, as shown in FIG. 18B, the shaft 43 to bedisposed in the hollow space consists of two shafts, i.e., shafts 43 aand 43 b. The shaft 43 a is disposed so that the central axis thereofcoincides with the central axis of a core to be formed. On the otherhand, the shaft 43 b is disposed next to the shaft 43 a so as to be inparallel with the shaft 43 a. The shafts 43 a and 43 b are formed of aresin material as in Embodiment 1. However, the material of the shafts43 a and 43 b is not limited to a resin material.

Next, as shown in FIGS. 19A and 19B, the hollow space where the shafts43 a and 43 b are disposed is filled with a fusible material 44. Also inEmbodiment 4, paraffin wax is used as the fusible material 44, and afterthe injection, the fusible material 44 is left at room temperature untilit is solidified, as in Embodiment 1.

After that, as shown in FIGS. 20A and 20B, the bonded core formationmolds 41 and 42 are separated from each other to obtain a core 46. Thecore 46 includes three thin tube portions 46 a and a main tube formationportion 46 b. Also in Embodiment 4, only the main tube formation portion46 b is formed of the fusible material as in Embodiment 1. The thin tubeportions 46 a are formed of the shaft 43 a or 43 b only. In Embodiment4, polishing the core also is required.

Subsequently, as shown in FIGS. 21A and 21B, an arc tube body formationmold 47 having a recess 47 a and an arc tube body formation mold 48having a recess 48 a are provided, and the core 46 is disposed in ahollow space formed by the recesses 47 a and 48 a. Thus, a space 45 forforming an arc tube body is formed between the respective recesses 47 a,48 a and the core 46. In Embodiment 4, the recesses 47 a and 48 a alsoare formed considering the shrinkage of an arc tube body after firing,and the arc tube body formation molds 47 and 48 also are formed ofstainless steel, as in Embodiment 1. Further, Embodiment 4 employs aplate member for positioning and positioning pins as used in Embodiment1 to improve the accuracy of the position adjustment of the core 46,although they are not shown in the drawing.

Next, as shown in FIGS. 22A and 22B, a slurry 50 containing ceramicpowder, a solvent, and a hardening agent as main components is injectedinto the space 45. After the slurry 50 is injected, the arc tube bodyformation molds 47 and 48 are left at room temperature to form ahardened slurry 51. The slurry 50 is the same slurry as that used inEmbodiment 1. Subsequently, as shown in FIGS. 23A and 23B, the arc tubebody formation molds 47 and 48 are separated to take out the hardenedslurry 51 integrated with the core 46.

Further, as shown in FIG. 24, the shafts 43 a and 43 b are pulled outfrom the hardened slurry 51 integrated with the core 46. In Embodiment4, the shafts 43 a and 43 b also may be formed of a material thatgenerates heat when a current is applied thereto, e.g., a nichrome wireand the like. When the shafts 43 a and 43 b are formed of such amaterial, it is possible to melt the fusible material 44 by applying acurrent, which allows the shafts 43 a and 43 b to be pulled out easily.

Subsequently, the fusible material 44 remaining inside the hardenedslurry 51 is drained from the hardened slurry 51, as shown in FIG. 25.In Embodiment 4, the hardened slurry 51 also is placed in a constanttemperature bath to drain the fusible material 44, as in Embodiment 1.Then, an organic constituent contained in the hardened slurry 51, whichis hollow after the fusible material 44 has been drained, is decomposedand evaporated off, and the hardened slurry 51 is subjected topre-firing and further to firing so that the hardened slurry 51 issintered, in the same manner as that in Embodiment 1. Thus, an arc tubebody 52 as shown in FIG. 26 is obtained.

In the arc tube body 52 shown in FIG. 26, reference numerals 52 a and 52c denote thin tube portions for accommodating electrodes, and referencenumeral 52 b denotes a main tube portion to serve as a discharge space.The thin tube portion 52 c is designed so as to accommodate twoelectrodes, and can accommodate an auxiliary electrode in addition to amain electrode. The main electrode in the thin tube portion 52 c and theother main electrode in the thin tube portion 52 a are disposed so as toface each other on a common straight line.

As described above, the method for manufacturing an arc tube bodyaccording to Embodiment 4 also is characterized in that a core includinga shaft at thin tube formation portions is used, similarly to the methodaccording to Embodiment 1. Therefore, Embodiment 4 can produce the sameeffects as those described in Embodiment 1.

Furthermore, 100 samples of the arc tube body including thin tubeportions capable of accommodating an auxiliary electrode and a mainelectrode as shown in FIG. 33B were manufactured according to theconventional method by connecting the respective components, and then,100 samples of a metal vapor discharge lamp were manufactured usingthese samples to conduct a life test. As a result, it was found that 5out of 100 samples had cracks in the connecting portions between therespective components.

The same life test was conducted with respect to 100 samples of the arctube body manufactured according to the method of Embodiment 4. As aresult, it was found that none of the sample arc tube bodies had cracks.Thus, it is understood that an arc tube body manufactured by the methodaccording to Embodiment 4 has good quality.

Embodiment 5

Hereinafter, a method for manufacturing an arc tube body and a core usedin the method according to Embodiment 5 will be described with referenceto FIGS. 27A and 27B to 29A and 29B. FIGS. 27A and 27B to 29A and 29Bare cross-sectional views, each illustrating one process of the methodfor manufacturing an arc tube body according to Embodiment 5. It is tobe noted that the processes illustrated from FIGS. 27A and 27B throughFIGS. 29A and 29B are a series of processes. Further, in FIGS. 27A and27B to 29A and 29B, FIGS. 27B to 29B are cross-sectional views takenalong the cutting plane line (line G-G′ to line I-I′) of FIGS. 27A to29A.

The method of Embodiment 5 is the same as that of Embodiment 4 exceptthat a layer of a fusible material or a combustible material covers ashaft also at thin tube formation portions of a core. An arc tube bodymanufactured by the method of Embodiment 5 is similar to the arc tubebody shown in FIG. 26.

First, as shown in FIGS. 27A and 27B, a core formation mold 61 having arecess 61 a and a core formation mold 62 having a recess 62 a are bondedto each other, and shafts 63 a and 63 b are disposed in the hollow spaceformed by the recesses 61 a and 62 a.

Similarly to the core formation molds used in Embodiment 1, the recesses61 a and 62 a are formed considering the shrinkage of an arc tube bodyafter firing. In Embodiment 5, the core formation molds 61 and 62 alsoare formed of stainless steel. However, as in Embodiment 1, the materialof the core formation molds 61 and 62 is not limited to stainless steel.Unlike Embodiment 1, core wires formed of stainless steel are used asshafts 63 a and 63 b. Further, unlike Embodiments 1 and 4, the shafts 63a and 63 b are not in contact with the recesses 61 a and 62 a.

Next, as shown in FIGS. 28A and 28B, the hollow space where the shafts63 a and 63 b are disposed is filled with a fusible material 64. Also inEmbodiment 5, paraffin wax is used as the fusible material 64 as inEmbodiment 1. The fusible material 64 is injected into the hollow spacethrough an inlet 65. After the injection, the core formation molds 61and 62 into which the fusible material 64 is injected are left untilthey cool down to room temperature so that the fusible material 64 issolidified.

After that, as shown in FIGS. 29A and 29B, the bonded core formationmolds 61 and 62 are separated from each other to obtain a core 66. Thecore 66 thus obtained includes three thin tube formation portions 66 aand a main tube formation portion 66 b, similarly to the core 46 used inEmbodiment 4. However, Embodiment 5 differs from Embodiment 4 in thatthe thin tube formation portions 66 a also are formed using the fusiblematerial 64.

In Embodiment 5, the inlet 25 is not provided so that the material flowsinto the main tube formation portion 66 b as in Embodiment 4. Therefore,the necessity of polishing the core is eliminated in Embodiment 5 as inEmbodiment 2. It is to be noted that, in Embodiment 5, the inlet 65 maybe provided so that the material flows into the main tube formationportion 66 b as in Embodiment 4. In this case, it is still possible toobtain the core 66 in which not only the main tube formation portion 66b but also the thin tube formation portions 66 a are formed using thefusible material 64 as shown in FIGS. 29A and 29B.

Thereafter, the thus-obtained core 66 is disposed in arc tube bodyformation molds; a slurry is injected into the arc tube body formationmolds and solidified; the hardened slurry integrated with the core istaken out from the arc tube body formation molds; and the hardenedslurry integrated with the core is fired after the core has beenremoved, in the same manner as that in Embodiment 4 (see FIGS. 21 to25). Thus, an arc tube body similar to that of Embodiment 4 can beobtained (see FIG. 26). The slurry used in Embodiment 5 is the same asthat used in Embodiment 1.

As described above, the method for manufacturing an arc tube bodyaccording to Embodiment 5 also is characterized in that a core includinga shaft at thin tube formation portions is used, similarly to the methodaccording to Embodiment 1. Therefore, Embodiment 5 can produce the sameeffects as those described in Embodiment 1. In addition, Embodiment 5can produce the effects peculiar to Embodiment 2 since the layer of thefusible material covers the shaft also at thin tube formation portionsof the core.

Embodiment 6

Hereinafter, a method for manufacturing an arc tube body and a core usedin the method according to Embodiment 6 will be described with referenceto FIG. 30. FIG. 30 is a cross-sectional view illustrating one processof the method for manufacturing an arc tube body according to Embodiment6. The method of Embodiment 6 is the same as that of Embodiment 5 exceptthat core formation molds are formed of a rubber material.

First, core formation molds 71 (see FIG. 30) having the same shape asthe core formation molds shown in FIGS. 27A and 27B of Embodiment 5 areformed using silicone rubber. Then, in the core formation molds 71formed of silicone rubber, ceramic core wires having the same shape asthose shown in FIGS. 27A and 27B are disposed as shafts 73 a and 73 b(see FIG. 30).

Next, as shown in FIG. 30, the hollow space formed by the core formationmolds 71 where the shafts 73 a and 73 b are disposed is filled with thesame spray-dry granule powder as that used in Embodiment 3, which isprepared by mixing carbon power with a butyral resin as a binder. It isto be noted here that, although two core formation molds actually areused as the core formation molds 71, only one of them is shown in FIG.30.

Subsequently, so-called rubber pressing is performed by applying apressure of 1800 kg/cm² to the side faces 71 a and 71 b of the coreformation molds 71 isostatically and hydrostatically. Thereafter, thecore formation molds 71 are separated from each other to obtain a corehaving the same shape as the core shown in FIG. 26 of Embodiment 5.

Thereafter, the thus-obtained core is disposed in arc tube bodyformation molds; a slurry is injected into the arc tube body formationmolds and solidified; and the hardened slurry integrated with the coreis taken out from the arc tube body formation molds, in the same manneras that in Embodiment 5. Subsequently, removal of the shafts,decomposition of carbon, and firing of the hardened slurry are performedin the same manner as that in Embodiment 3. Thus, an arc tube bodysimilar to that of Embodiment 5 can be obtained (see FIG. 26). Theslurry used in Embodiment 6 is the same as that used in Embodiment 1.

As described above, the method for manufacturing an arc tube bodyaccording to Embodiment 6 also is characterized in that a core includinga shaft at thin tube formation portions is used, similarly to the methodaccording to Embodiment 1. Therefore, Embodiment 6 can produce the sameeffects as those described in Embodiment 1.

Embodiment 7

Hereinafter, a method for manufacturing an arc tube body and a core usedin the method according to Embodiment 7 will be described with referenceto FIG. 31. FIG. 31A is a view of a core used in a method formanufacturing an arc tube body according to Embodiment 7, and FIG. 31Bis a view of an arc tube body manufactured by the method formanufacturing an arc tube body according to Embodiment 7.

As shown in FIG. 31A, in Embodiment 7, a core 80 is provided with threeshafts, i.e., shafts 81, 82, and 83, and thin tube formation portionsare formed of these three shafts 81, 82, and 83. The shaft 81 is notdisposed so as to be on a common straight line with the shaft 82 or 83.

Therefore, by conducting the injection of a slurry and the firing in thesame manner as that in Embodiment 4 using the core 80, an arc tube body85 as shown in FIG. 31B is obtained. In FIG. 31B, reference numerals 85a and 85 c denote thin tube portions, and reference numeral 85 b denotesa main tube portion. The thin tube portion 85 c is designed so as toaccommodate two electrodes, and can accommodate an auxiliary electrodein addition to a main electrode. Unlike the arc tube body shown in FIG.26, in the arc tube body 85 manufactured using the core 80, the mainelectrode in the thin tube portion 85 a and the other main electrode inthe thin tube portion 85 c are not disposed so as to face each other ona common straight line.

Embodiment 8

Hereinafter, a method for manufacturing an arc tube body and a core usedin the method according to Embodiment 8 will be described with referenceto FIG. 32. FIG. 32A is a view of a core used in a method formanufacturing an arc tube body according to Embodiment 8, and FIG. 32Bis a view of an arc tube body manufactured by the method formanufacturing an arc tube body according to Embodiment 8.

As shown in FIG. 32A, in Embodiment 8, a core 90 also is provided withthree shafts, i.e., shafts 91, 92, and 93, and thin tube formationportions are formed of these three shafts 91, 92, and 93, as inEmbodiment 7. The shaft 91 is not disposed so as to be on a commonstraight line with the shaft 92 or 93. Embodiment 8 differs fromEmbodiment 7 in that the shafts are not in parallel with each other.

Therefore, by conducting the injection of a slurry and the firing in thesame manner as that in Embodiment 4 using the core 90, an arc tube body95 as shown in FIG. 32B is obtained. In the arc tube body 95, the thintube portions 95 a, 95 c, and 95 d are not in parallel with each other.The thin tube portions 95 a and 95 c accommodates main electrodes whilethe thin tube portions 95 d accommodates an auxiliary electrode.

INDUSTRIAL APPLICABILITY

As specifically described above, a method for manufacturing a arc tubebody according to the present invention and a core according to thepresent invention can reduce the chances that thin tube formationportions of the core and thin tube portions of the arc tube body mightbe broken and thus can improve the productivity of an arc tube body.Further, the dimensional accuracy of the thin tube portions of the arctube body also can be improved. Furthermore, the degree of freedom inthe design of the internal shape of the thin tube portions of the arctube body also can be increased, and the necessity of mechanicalprocessing required when changing the thickness of the arc tube body inconventional methods is eliminated, resulting in cost saving.

1-9. (canceled)
 10. A core used for manufacturing an arc tube body,which comprises a main tube portion to be a discharge space and thintube portions for accommodating electrodes, using a pair of molds and amaterial to be injected thereinto, the core being disposed in a hollowspace formed by the pair of molds before injecting the material,comprising: portions for forming an internal shape of the thin tubeportions; a portion for forming an internal shape of the main tubeportion; and a shaft disposed in the portions for forming an internalshape of the thin tube portion.
 11. The core used for manufacturing anarc tube body according to claim 10, wherein the portion for forming aninternal shape of the main tube portion is formed of a fusible materialor a combustible material.
 12. The core used for manufacturing an arctube body according to claim 10, wherein the core comprises two portionsfor forming an internal shape of the thin tube portions, one of the twoportions facing the other portion with the portion for forming the maintube portion intervening therebetween, and a shaft present at one of thetwo portions and a shaft present at the other portion are defined by onecommon shaft.
 13. The core used for manufacturing an arc tube bodyaccording to claim 10, wherein the core comprises at least two shafts.14. The core used for manufacturing an arc tube body according to claim10, wherein the portions for forming an internal shape of the thin tubeportions are formed by forming a layer of a fusible material or acombustible material around the shaft.
 15. The core used formanufacturing an arc tube body according to claim 10, wherein the shaftis formed of a metallic material, a resin material, or a ceramicmaterial.
 16. The core used for manufacturing an arc tube body accordingto claim 10, wherein the shaft is formed of a material that generatesheat when an electric current is applied thereto.